ASHINGTON - The endgame of the presidential campaign was supposed to work like this: Al Gore and George W. Bush would spend nearly every waking hour in a handful of ''battleground'' states where the race was closest, angling for the vote of the ever-shrinking pool of undecided voters.
But with the two major-party candidates as close as ever in the polls, and with Green Party nominee Ralph Nader pulling enough support to swing the outcome in several states, the presidential battlefield has unexpectedly widened.
Unlike most recent presidential campaigns, the endgame is not concentrated solely on some Midwestern battlegrounds, and the usual group of five or six hotly contested states has grown to 21 in the last few weeks.
At the same time, the strategy has turned from courting undecided voters to ensuring that every known supporter shows up at the polls.
All of this is occurring as groups ranging from the political parties to unions to big business are launching the largest last-minute expenditure of money ever seen in a presidential race, much of it focused on bolstering turnout among key voting groups in tightly targeted precincts.
With the debates already a faded memory, the campaign is a three-pronged war: repeated candidate visits to key states, a massive voter-turnout drive, and a flood of television advertisements. Ground zero for the campaign is in places such as Scranton, Pa., where the local ABC-TV affiliate, WNEP, exemplifies the explosion in political advertising being hurled at viewers.
''We have never seen anything like it,'' said the station president, Rene Laspina. ''It is four or five times as much as other years. Almost all the ads on every news show and every prime-time show are political. This is a once-in-a-lifetime event.''
Multiply the Scranton experience by dozens or perhaps hundreds of other key communities in states from Florida to Wisconsin to Oregon, and the frenzy over the finale becomes clear.
Bush is spending heavily in Florida, where he once thought he was a sure thing with his brother Jeb as governor, while Gore is investing resources everywhere from his home state of Tennessee to the usual Democratic bastions of Oregon and Washington.
In just the last four days, both campaigns have made decisions to spend significantly in states that were deemed off the table until recently. Bush is buying advertisements in California and Illinois, two states where Gore once had a safe lead. Bush campaigned in Illinois last week and plans to appear in California tomorrow.
Gore, meanwhile, is increasing his advertising in the Pacific Northwest and is considering buying advertising in three states his campaign previously had written off: Georgia, North Carolina, and Kentucky. It may be too late to make headway in the three Southern states, but the closeness of the contests has convinced some Gore aides that every possible state should be in play.
''This is such an odd election because the targets are actually broadening. Instead of focusing more dollars in fewer markets, the campaigns are focusing more dollars on more markets,'' said Ken Goldstein of the University of Wisconsin in Madison, who has studied the nationwide presidential campaign advertising.
Potential new battlegrounds seem to pop up daily. New Jersey, once thought to be among the safest of states for Gore, has tightened to a six-point race, according to a Quinnipiac College survey.
''I'm concerned about the presence of Ralph Nader,'' said Thomas Giblin, chairman of the New Jersey Democratic Party. ''He will get 4 or 5 percent. I don't think there is any room to be overconfident.'' Giblin said that while he would like Gore to visit the state, ''I haven't asked because New Jersey is pretty far down the pecking order.''
Minnesota, another presumed Gore haven, is now statistically tied, with Nader a big factor at 10 percent, according to a St. Cloud University poll. West Virginia, also usually reliably Democratic, is in the questionable column, partly due to Bush's warning about the impact of Gore's environmental plans on the state's coal industry.
While the campaigns are being spread thin, the political parties and independent groups are more than making up the difference. The Bush and Gore campaigns theoretically are confined to spending $68 million each in federal money for the general election. But both parties have tens of millions of dollars in unregulated ''soft money'' to buy advertisements and get out the vote.
On the 6 p.m. news in Scranton last week, a typical half-hour included a Democratic Party ad that said Bush's Social Security plan would break promises to seniors, a Bush ad that promoted tougher standards in schools, and an indirect attack on Gore's stance on gun control by a group identified as ''www.voteyoursport.com.'' The ad, which features the stars being torn off the American flag, is paid for by the firearms industry, although that is not revealed on the Web site.
But some of the most important action is not on the airwaves. The National Rifle Association, which is spending $20 million to influence the election - twice its 1996 amount - is putting most of its money into the effort to get its 4.1 million members to the polls to vote for Bush.
''We will do everything short of skywriting to get our members to the polls, and if I thought skywriting would work, I'd do that, too,'' said NRA chief lobbyist Jim Baker. The NRA has reworked its strategy to focus on states such as Tennessee and West Virginia.
One of the biggest late spenders, the AFL-CIO, is putting nearly all of its money into efforts to get out identified supporters. Less than 10 percent of organized labor's money at this point is going into television commercials. The labor organization, like many interest groups, believes it is not cost-effective at this late date to try to sway undecided voters, many of whom either are likely to stay out of the election or split evenly among the candidates. It is far more effective to spend money to bring out committed supporters to the polls, according to AFL-CIO political director Steve Rosenthal.
''At this stage of the game, the major focus should be getting out the vote,'' Rosenthal said. ''I think a fair number of undecided voters will stay home. We have identified who are union supporters.''
The AFL-CIO is mostly interested in turning out union members who will support Gore. But while much has been made of Gore's union support, it is hardly monolithic. President Clinton had the support of 59 percent of union members who voted in 1996, and Gore's support might be lower, especially because Nader is wooing labor voters who disagree with Gore's support of free-trade deals.
But even if the AFL-CIO can match the 1996 showing for Clinton, that may not be enough for Gore. While the labor strategy will help in states such as Michigan, where as many as 40 percent of the voters may be union members, it will be far less effective in many states that have emerged as new battlegrounds. For example, the union membership in Arkansas is minuscule, and it is only about 9 percent in Tennessee and Florida. Thus, if Gore is counting on labor to bring him to victory, it may not be enough.
Similarly, Gore is counting on a record turnout among blacks. While that would help in traditional battlegrounds such as Michigan, where 15 percent of the population is black, it will mean less in some of the emerging key states. For example, the black population is only 1 percent in New Hampshire, 2 percent in Oregon, and 3 percent in Minnesota.
Gore's biggest concern as he heads toward Election Day is that he has apparently lost ground among women. A CNN/USA Today/Gallup poll completed late last week found that Gore was leading Bush among women by only 1 percentage point. Bush's lead among men was 16 percentage points. In order for Gore to win, he almost certainly needs much stronger support among women. Clinton won in 1996 with a 17-point lead among women.
To that end, the National Abortion and Reproductive Rights Action League, which believes that support of abortion rights will help Gore, is running television advertisements highlighting the vice president's record. The league's ads also urge those who are thinking of supporting Nader to vote instead for Gore because of the abortion issue. Bush opposes abortion rights.
As the battlegrounds continue to shift, the campaigns will unload the remainder of their war chests. Of the $68 million in federal funds that Bush and Gore have each received, each has about one-third left to spend. But the Republican Party has a modest advantage in unregulated ''soft money'' funds, and the business groups have more money on hand than organized labor. In the battleground states, the problem won't be finding money to spend, but rather finding prime-time airtime left for the commercials.
Some of the most experienced political observers warn that the race is just too fluid to predict the outcome. ''There are 15 states with a three-point difference,'' said Charles Cook of the Cook Political Report. ''I wouldn't bet more than a buck on Bush at this point. We are on a white-knuckle ride here.''
